From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Dyno Sheet
Date: Sat, 8 Aug 2020 09:50:14 +0800
References: <list-617412@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-617412@logan.com>
Message-Id: <2B284A5A-27B9-4E02-A4BA-637543D49F73@gmail.com>

So Finn. The fuller story is.

I=E2=80=99m thinking I need to make up a string of 5 amps for my 5 =
transducers that I have already, to condition the few millivolts to =
0-3.3v for a pic micro or the sort.
Then I=E2=80=99m thinking how do I read and log the data.
But I=E2=80=99d like it synced with the dynon log data which is =
brilliant.
Look at a graph with pressures along side temps and speeds and =
altitudes=E2=80=A6..

And then I think of the abundant excess EGT inputs that are used to that =
kind of millivolt input all connected and logged and displayable. Just a =
bit of configuration and basically no circuit and development time =
required.

Is it to good to be true. Maybe, but indications are its too easy.

Brilliant if it works.

Steve


> On 8 Aug 2020, at 9:39 am, Stephen Izett stephen.izett@gmail.com =
<flyrotary@lancaironline.net> wrote:
>=20
> Hi Finn
> I input a polynomial based on the raw data from the transducer data =
sheet.
> Full scale output is 35mV for 1.45psi.
> Offset at 0 reading is on average 20mV.
>=20
> But I thought I=E2=80=99d create a polynomial based on a new set of =
data using the water manometer incase the 'junction flux capacitor' was =
throwing out the readings to far.
> To far would be pretty far, as I=E2=80=99m simply wanting rough =
numbers for comparison as I play with the cowl flaps etc.
>=20
> Does that make sense?
>=20
> Steve
>=20
>=20
>=20
>> On 8 Aug 2020, at 9:14 am, Finn Lassen finn.lassen@verizon.net =
<flyrotary@lancaironline.net> wrote:
>>=20
>> Oh, I thought you'd already worked out the polynonmial values.
>>=20
>> =
http://www.mosaic-industries.com/embedded-systems/microcontroller-projects=
/temperature-measurement/thermocouple/calibration-table#computing-cold-jun=
ction-voltages
>>=20
>> probably way overkill.
>>=20
>> Input from a  type K (EGT) thermocouple would expect  a maximum of =
55mV (1370C +).
>>=20
>> So you may need a voltage divider, depending on the max expected =
outputs from the pressure sensors.
>> Then the trick will be to come up with a formula to counteract the =
chip's calculation.
>>=20
>> For the MAX6675 used in the EM3, it appears fairly simple:
>> The MAX6675 includes signal-conditioning hardware to
>> convert the thermocouple=E2=80=99s signal into a voltage compatible
>> with the input channels of the ADC. The T+ and T-  inputs
>> connect to internal circuitry that reduces the introduction
>> of noise errors from the thermocouple wires.
>> Before converting the thermoelectric voltages into
>> equivalent temperature values, it is necessary to compensate
>> for the difference between the thermocouple
>> cold-junction side (MAX6675 ambient temperature) and
>> a 0=C2=B0C virtual reference. For a type-K thermocouple, the
>> voltage changes by 41=CE=BCV/=C2=B0C, which approximates the
>> thermocouple characteristic with the following linear
>> equation:
>> VOUT =3D (41=CE=BCV / =C2=B0C) =E2=9C=95 (TR - TAMB)
>> Where:
>> VOUT is the thermocouple output voltage (=CE=BCV).
>> TR is the temperature of the remote thermocouple junction
>> (=C2=B0C).
>> TAMB is the ambient temperature (=C2=B0C).
>>=20
>> Fortunately one of the channels in my EM3 is the temp of the PCB =
where the chip is located (TAMB).
>>=20
>> Don't know what chips are used in the Dynon Skyview.
>>=20
>> Finn
>>=20
>>=20
>> On 8/7/2020 7:14 PM, Stephen Izett stephen.izett@gmail.com wrote:
>>> Hi Finn.
>>>=20
>>> The pressure transducers I have can measure from memory a =
differential pressure of about 40=E2=80=9D of water.
>>> They have a millivolt output and in the process of cooking up a set =
of amps and thinking about the fact that Ive used up all my Engine =
Monitor inputs I pondered all those unused EGT and CHT inputs with =
amplifiers for millivolt input.
>>> I thought about the thermocouple compensation, impedance matching =
and common mode currents from the egt amps (don't really have a handle =
on these) and decided I probably wouldn't damage them!
>>> So I just thought Id try it out.
>>> I wired one straight to an egt input and the Dynon 5v supplied, and =
applied some lung pressure and the dynon display showed some life.
>>> I reworked a new Polynomial and she seems to provide a linear output =
over my lung burst pressure which from memory is a little over 1 psi.
>>> I=E2=80=99m not after certifiable numbers but have built a manometer =
to hopefully roughly calibrate the output by playing with the =
Polynomial.
>>> So lots of ignorance as far as what=E2=80=99s happening with the =
electrons at the interface but the results look promising and could be =
so much more helpful and easier than rigging a manometer in the cockpit.
>>>=20
>>> Happy to have my party spoilt by someone with knowledge of the =
compensation circuit used in the EGT amps.
>>>=20
>>> Cheers
>>>=20
>>> Steve
>>>=20
>>>=20
>>>=20
>>>=20
>>>=20
>>>=20
>>>> On 7 Aug 2020, at 11:01 pm, Finn Lassen finn.lassen@verizon.net =
<flyrotary@lancaironline.net> wrote:
>>>>=20
>>>> On 8/7/2020 10:00 AM, Stephen Izett stephen.izett@gmail.com wrote:
>>>>> I worked out that they interface quite nicely without any other =
circuitry with the Dynon Skyview's surplus EGT inputs via a new =
Polynomial in the sensor config settings.
>>>> I'm thinking of using my unused?? EGT inputs for current (Hall) =
sensors.
>>>>=20
>>>> How did you compensate for the EGT compensation?
>>>>=20
>>>> Finn
>>>>=20
>>>>=20
>>>> ---
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>=20
>=20
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